1. Technical Field
The present invention relates to techniques of controlling distribution of information via a network and the like.
2. Background Art
In recent years, with the widespread use of digital cameras, camera mobile phones, and the like, individual users become able to create digital content such as a still image or a moving image easily, and an environment where personal content, i.e. digital content created by an individual user, can be transferred to a digital television, a hybrid recorder, a portable device, or the like and submitted for viewing is increasingly improved. This provides more opportunities for family members or friends to exchange personal content with each other. Hence the distribution of personal content is expected to be more actively performed in the future.
As one example of such personal content distribution systems, non-patent document 1 discloses a peer-to-peer file exchange system. In this file exchange system, users on a network exchange personal content. A user who requests personal content uses his/her own terminal to indicate desired personal content to a terminal of a user who possesses the personal content, and downloads the personal content via the network. In the peer-to-peer file exchange system, the user who receives the personal content can freely re-deliver that personal content to another user (secondary delivery). In this way, the personal content is actively distributed.
However, once the personal content is output to the network, it becomes difficult to restrict the use of the personal content.
To solve this problem, patent document 1 discloses the following technique, with the aim of ensuring profits of content writers, content providers, and the like. According to this technique, a secure container having sales condition information (UCP) that determines a sales condition of content between user devices is established. The UCP includes UCP secondary delivery permitted number information as information about an upper limit of the number of parallel content distributions between user devices. A user device that purchases the container generates use control information (UCS) including the UCS secondary delivery permitted number information which specifies the number of content distributions, and stores it on a memory. At the time of secondary delivery of the content, the user device executes a condition check process on the UCS secondary delivery permitted number information. The delivery of the content is permitted only when the condition is satisfied, and prohibited when the upper limit of the number of distributions is exceeded.
Non-patent document 1: Naoki Ito “P2P Computing—Technical Description and Application” Soft Research Center Inc., December 2001.
Patent document 1: Japanese patent application publication No. 2001-256413.